Effect of dye concentrations in blended-layer white organic light-emitting devices based on phosphorescent dyes.

摘要

The electronic and optoelectronic behavior of white organicud light-emitting devices (OLEDs) based on blue (FIrpic) and redud [Ir(piq)(2)(acac)] phosphorescent dyes doped into the same layer of aud polyvinylcarbazole (PVK) host are reported. The conductivity of all theud OLEDs studied appeared to be dominated by space-charge injectionud effects, exhibiting a current I versus voltage V dependence of the formud I alpha V-n, with n approximate to 7 at applied voltages at whichud electroluminescence was observed. Systematic studies of the currentud versus voltage and light-emitting behavior of the OLEDs have identifiedud different excitation processes for the two dyes. It is suggested thatud electroluminescence from the FIrpic molecules originates by directud transfer of the exciton energy from the PVK to the dye molecules, whileud the process of light emission from the Ir(piq)(2)(acac) moleculesud involves carrier trapping. The efficiency of the devices can be tuned,ud to some extent, by varying the thickness of the organic film. Luminousud efficiencies and luminous power efficiencies of 8 cd A(-1) and 3 lm W-1ud were measured for these blended-layer OLEDs, with Commissionud Internationale de l'Eclairage coordinates of 0.35, 0.35. ud